The use of vacuum for investment casting is well known by the use of a flask, which is a permeable frame, into which the slurry is poured after the wax model has been mounted. The flask is generally perforated with a flange at one edge that fits in a way that prevents vacuum leakage. After drying and heating, the flask is mounted in a vacuum chamber, which enables a pressure difference effect.
There is known a variety of systems, methods and accessories for investment casting, some examples of which are disclosed below:
U.S. Pat. No. 4,825,934 to Kai suggested a cushioning sheet made of flammable material. It is inserted into a casting frame and adapted so that it burns out when heated to leave a space between the casting frame and the casting mold.
U.S. Pat. No. 5,896,913 to Grandi suggested Investment casting paper and guard. The paper acts as both vacuum liner and splash guard. It is fabricated as a perforated paper sheet having hooks which is inserted in a cylindrical manner into the casting flask and burns out when heated.
U.S. Pat. No. 4,915,155 to Martin suggested a solution to annul the vacuum chamber. An integral casting flask/vacuum chamber combination is disclosed in which an inner perforated tube forming the casting flask is disposed coaxially inside of an outer tube, thus forming a vacuum chamber between the two tubes.
Another alternative to eliminating the need for the flask was suggested by EP1027180 to Ashton. It consists of placing the shell in a mold box and surrounding it with granular filler, vibrating the box to compact the filler to a high bulk density and then applying a vacuum to the granular filler.
In order to get a uniform and controlled atmosphere, several machines with vacuum valves have been developed in a way that protective gas can be used before the vacuum process.
U.S. Pat. No. 4,784,207 to Maio suggested an apparatus for lost wax castings wherein metal is melted in a vacuum vessel, and wherein there are provided vacuum pumps for producing a higher degree of vacuum around the mold during casting.
GB774287 to Turnbull suggests a method in which a shell is positioned within an evaluable container and a thin diaphragm of suitable material, for example stainless steel for the production of steel alloy casting, is positioned so as to extend across a pouring throat for the entry of the casting material to the interior of the mold. In the pouring operation the molten metal accumulates above the diaphragm, which does not melt immediately. The metal is poured thereon, so that the slag and any air entrained in the metal will rise to the surface. When the diaphragm melts the metal flows into the mold cavity.
U.S. Pat. No. 4,579,166 to Neelameggham suggested impregnation of at least the pores adjacent to the mold cavity with pressurized gas as a principal inhibiting agent, using a purge cup which fits tightly over the sprue.
Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.